Reverse osmosis (RO) is a purification method that forces water through a semi-permeable membrane to remove contaminants. This process is highly effective, producing water that is nearly free of all dissolved solids (TDS), making it a popular choice for high-purity drinking water globally. However, this aggressive purification raises a significant concern regarding the long-term consumption of the finished product, often called demineralized water. The central issue is that the technology is non-selective, removing beneficial, naturally occurring minerals alongside harmful substances. The debate centers not on RO water’s purity, but on its lack of nutritional content and its chemical properties.
How Reverse Osmosis Removes Essential Minerals
The efficacy of reverse osmosis relies on a dense, synthetic semi-permeable membrane that acts as a molecular sieve. Water is pushed across this membrane under high pressure, allowing only water molecules to pass through to the permeate side. The membrane pores are rated for filtration down to 0.0001 microns, effectively blocking larger particles, including bacteria, viruses, and chemical contaminants.
The process is indifferent to the chemical nature of the dissolved particles it rejects; it cannot distinguish between a harmful heavy metal and a beneficial mineral ion. Essential minerals, such as calcium and magnesium, exist as dissolved salts. Their ionic size is too large to pass through the membrane, meaning RO systems achieve a contaminant removal rate of over 95% for both harmful substances and desirable mineral content, leaving the water substantially demineralized.
Health Consequences of Demineralized Water Intake
The consumption of water stripped of its mineral content can pose specific health risks, particularly when water is a person’s primary source of certain nutrients. The World Health Organization (WHO) has noted that long-term consumption of water low in calcium and magnesium is not appropriate for drinking without further enrichment. These two minerals are particularly important, and their presence in water contributes to overall dietary intake.
A lack of these minerals in drinking water has been tied to an increased risk of specific health issues, including a higher rate of death from cardiovascular diseases. Magnesium plays a role in over 300 enzyme reactions in the human body, and its deficiency can lead to an electrolyte imbalance, which may manifest as fatigue, muscle cramps, and heart irregularities. Furthermore, low mineral water intake may be associated with decreased bone density in adults and a higher risk of bone fractures in children.
The body’s homeostatic mechanisms are challenged by demineralized water, as the lack of electrolytes can cause an imbalance in the fluid distribution inside and outside of cells. When cooking with demineralized water, it can also pull minerals out of the food itself, with losses of calcium and magnesium sometimes reaching as high as 60%. This loss reduces the nutritional value of prepared meals, further contributing to a potential mineral deficit.
The Solvent Effect: Why Pure Water Can Be Problematic
Water is often referred to as the universal solvent because its molecules are highly polar, allowing it to dissolve more substances than almost any other liquid. When water is purified to a near-zero total dissolved solids (TDS) level by reverse osmosis, it becomes an aggressive or “hungry” solvent. This highly pure water seeks to re-establish a mineral balance by dissolving materials it comes into contact with.
This solvent property presents two main concerns. The first is the potential for the water to leach minerals from the body’s own tissues during digestion. To balance the electrolyte concentration, the intestinal tract must add electrolytes to the ingested water, drawing them from the body’s reserves. The second concern relates to the plumbing, where the demineralized water can corrode metal pipes and fixtures, potentially dissolving trace amounts of materials like copper or lead. The consumption of this water, now contaminated by the plumbing system, can expose the user to undesirable metals.
Methods for Safe Reverse Osmosis Water Consumption
The solution to the drawbacks of reverse osmosis water is not to abandon the purification method, but to implement a process of remineralization. This involves reintroducing a balanced concentration of beneficial minerals back into the purified water. The most common method is to use a post-filter remineralization cartridge, installed as a final stage in the RO system.
These specialized cartridges typically contain mineral media, such as calcium carbonate or magnesium oxide, that slowly dissolve into the water as it passes through, restoring a healthy mineral composition and raising the pH. For users without an integrated system, simple methods include adding concentrated mineral drops, or blending a small amount of mineral-rich tap water with the RO water to achieve a desirable TDS level. Restoring the mineral content makes the water more palatable, healthier to consume, and less corrosive to plumbing.